Nitroglycerin is used to treat and prevent heart-related chest pain (angina). Angina occurs when the heart muscle is not getting enough blood. This medicine works by relaxing and widening blood vessels so blood can flow more easily to the heart. As with other nitrates used to treat anginal chest pain, nitroglycerin converts to nitric oxide (NO) in the body. NO then activates the enzyme guanylyl cyclase, which converts guanosine triphosphate (GTP) to guanosine 3',5'-monophosphate (cGMP) in vascular smooth muscle and other tissues.